1. Field
The embodiments discussed herein relate to video image processing, and, more particularly, to a technology that can prevent deterioration of image quality when enhancing the resolution of a predetermined key frame in a video sequence.
2. Description of the Related Art
The development of information and communication technologies (ICT) including the Internet has increased video communication as well as text and voice communications. As conventional text-oriented communication fails to satisfy various needs of consumers, multimedia services, which can provide various types of information such as text, images and music, are increasing. Due to its large size, multimedia data requires mass storage media. In addition, wide bandwidths are required to transmit the multimedia data. Accordingly, a compression coding method is a requisite for transmitting multimedia data including text, images, and audio.
The basic principle of data compression lies in removing data redundancy. That is, image data can be compressed by removing spatial redundancy which has to do with repetition of the same color or object in an image, temporal redundancy which occurs when there is little change between adjacent pictures in a moving image or when the same sound is repeated in audio, or perceptual redundancy which takes into consideration insensitivity of human eyesight and perception of high frequencies.
In a conventional video-coding method, temporal filtering based on motion compensation is used to remove temporal redundancy, and a spatial transform is used to remove spatial redundancy. A video coded using the conventional video coding method is transmitted to a variety of client devices, such as computers, digital televisions, and mobile phones, through a network. The client devices restore original video frames from the coded video in a decoding process corresponding to the coding process.
It is sometimes necessary to upsample the restored video frames (that is, enhance resolution of the restored video frames). For example, if the resolution of the restored video frames is lower than that of a display device that displays the restored video frames or that of a printer that is to print the restored video frames, the upsampling process is essential.
Specifically, if a photo-printer having a resolution of 300 dots per inch (dpi) is to print a video frame having a resolution of 640×480 pixels to a size of 4×6 inches, the resolution of the video frame has to be enhanced nearly three times its original resolution. Similarly, if a laser printer having a resolution of 600 dpi is to print the video frame at the above size, the resolution of the video frame has to be enhanced nearly six times its original resolution.
Generally, a conventional spatial upsampling method, such as bi-linear interpolation or bi-cubic interpolation, is used to upsample still images. On the other hand, video frames are upsampled using their adjacent frames which contain information very similar to the video frames, that is, temporal information. In addition, the upsampled video frames have very limited information compared to the original. Therefore, if the upsampled video frames are not properly upsampled, a resolution of the upsampled video frames deteriorates, and a blocking effect or ringing artifacts is highly likely to occur.
However, most conventional methods of upsampling video frames apply the spatial upsampling method, which is used to upsample still images, and fail to consider improving the upsampling performance using temporal information.